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Glad to hear I shouldn’t need to buy another slide. I do think I’d like to notch the front though, if it does make a slight improvement (though in all truth, I’m actually very pleased with everything down low).
Exactly how large in height, width, and in shape shape (rounded, triangular, squared), should the reed side opening be enlarged?
I am a bit confused on the needle though. I have a -73, and in all your recommendations you recommend a -75. I understand the difference between a 42 and 43 is a half clip step, but should I be running a -73 (skinnier... so richer), or should I’ll be ordering a -75 (fatter... so leaner). If I’m ordering the -75s, I’ll order one of each so I have the half step increments. Part two to that is the fact that I’m at 1.75 turns on the air screw. If I lean out to a -75, and also clean out the pilot jet, will that be too lean down low?
I’ll order the 42-75 and 43-75 needles.
I ordered all the pilot sizes from 30-45, and mains from 420-500, so I’ll throw in the really big main and try a smaller pilot though.
Thanks again!
The slide that you cut, sounds exactly as to how I cut mine. Here’s one that I cut today for someone.
It might be working for you with the 490 main jet though because its leaner through the main with a richer needle. It might even be close to the 75 needle in a 500 main. But for what you're giving up top end wise with the 490 vs. a 500 I think you'll be happier with the bigger jet setup and 43-75 needle.
I wouldn't be to concerned about the air screw. I check mine when I ride just to see if there is much difference and some days I'l at 1.5 turns and some days I'm at 1.75 turns, just depends on the air that day.
I feel much relieved now about the slide, and I’m gonna lower the pilot, raise the main, and order a couple -75 needles.
Thanks again!
PS... Digger, I see the slide you posted has a large curved reed side opening. Do you have any specs on how much you opened that up?..
PPS... How sensitive are our engines to running lean. My only real experience with worrying about air fuel ratio’s is on a turbocharged car... and I know it gets really bad, really quick when you go just a little lean (at wide open throttle/ under load). Low load, low RPM doesn’t really matter... but high load/ rpm does. The idea that the bike was running a 440 main (for the first 36 hours of its life), now a 470, and soon probably an ideal 500, just boggles my mind. I’m certain there’s not a one-to-one correlation, but 60 is about 12% of 500. If I ran my car 10% lean at wide open throttle it would probably only last a few pulls.
Bike seems to have very good compression, and was ridden primarily in the woods, but now I feel compelled to do a compression check just to make sure I didn’t wear anything out. Lol.
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Every time I hear, see, or think about things running lean, I have visions of holes in pistons, and rods windowing blocks, pop in my head. It’s just such a balancing act with a turbocharged car (at high horsepower)... And the consequences are quite expensive. I’ll try and relax, and just enjoy the ride. Lol
85 degrees sea level
35 pilot
43-75 needle 3rd clip
S4
470 main
I really didn’t want to change my jetting the last few years but I’ve had some issues with low end richness sounds like it’s running underwater so I made the above charges
Bike runs unbelievable, for anyone hesitant to make the changes I would highly recommend you try.
Change the clip position to a richer setting. Turn the air screw in and or change the pilot( richer/larger). Notch the front side of the slide like the above pic.
The jet block gasket really need to be replaced as well. you will also need the #5 slide.
The 42-71 needle is quite a bit richer than the 42-75, but shouldn't bog at the 1/4 throttle position, but it will run rough.
Do you have access to a dial/digital caliper and a round file ? Look at the slide above that I cut. That all you need to do is take 1mm off the off that arch and blend it in. It's pretty clear as to where I cut and blended. 1mm will get you to a 5.0 slide.
Pit Row
Bike specs:
-2017 KTM 150xcw
-RK Tek head insert (pump fuel, 1000' elevation, temps between 40-95F)
-FMF Fatty Pipe
-FMF Turbinecore 2.1 spark arrestor
-vforce 4 reeds
-TMX38 (jet block gasket/o-ring/float height adjusted/repaired)
-5.0 slide
-32.5 Pilot
-S4 needle jet
-42-74 needle
-3rd clip pos
-490 Main Jet
-Non ethanol 91 pump with Klotz TCW-3 @40:1
Now that I have it running great HERE.....
Im taking a trip out west to Colorado. Where most of our riding will be between 7000-8000 feet, with temps ranging from 65 in the mornings to about 85 in the afternoon. Low humidity, around 35% or so.
Digger / AJ565, do you have any advice for jetting on this trip? I looked at the jetting chart in the manual to get an idea of how much of a change they recommend going from 1000' to 8000', and from what I can tell, they recommend the following:
-Decreased the MJ one size
-Went to a 1/2 clip richer needle
-Dropped the needle clip 1 position (essentially leaning it out by 1/2 clip pos)
-1/2 turn richer ASO
-Pilot remained unchanged
Not sure if Im even close with my logic, but by doing that "formula" that would put me at roughly:
-32.5 pilot
-43-74 needle
-2 clip pos
-480 MJ
Sorry for the ramble and thank you in advance for your help.
Sorry, I don’t have any high altitude jetting notes for you. Time to chart new territory and report back what you find.
Took the bike out with stock jetting first for break in. 91 pump gas at 40:1 with Motorex. Motoland MX park, 1400ft elevation, AZ in August so 90-100 degrees and very low humidity. Bike was pretty blubbery and had a very distinct gurgle at about 1/4 throttle and a nice line of drool out the silencer. I was like, yep, there it is, as expected.
After 1 hr of rolling around on the kiddie track breaking it in I lowered the needle 1-clip, drained the fuel, and put VP MS-100 in at 40:1 with Maxima Super-M. Holy crap, totally different bike. Could not believe how big of a difference 1 clip and the fuel made. Clean, crisp, ripping and no drool. People say the KTM/Husky has weak bottom end compared to the YZ125 but it actually felt the same on bottom as my YZ125 and stronger on top.
Now that I've experienced that, and seeing that the jetting recommended in this thread works good on a 150XCW with a spark arrestor, I am a little concerned that jetting might be too lean for me if I keep using this MS-100 fuel, In general, I think this fuel tends to lean the jetting out or mask rich jetting.
As a side note, I also tried a PWK with STIC that I never could get running right in my YZ125. It seemed a bit better than in the YZ125 but I still saw some of the same symptoms (lean bog but then drooling if I try to richen it up). Tractor and others have told me this is likely due to the MS-100 oxygenated fuel. For some reason the STIC and oxy fuel don't seem to play well together. Well, that's another trial for another day. In the meantime, I am going to try the Digger jetting when this slide and other parts come in and see how it runs.
I agree with you that the bottom end is pretty strong on these bikes. Adjusting the power valve to 1 3/4 turns in from all the way out is a pretty noticeable improvement and will result in you abusing the clutch less out of a turn.
Question - What about the V-Force 4 reed block ? Would that be any different than the stock one, jetting wise?
2021 Husq TC125
100LL Avgas, Maxima Super-M 40:1
Vented airbox cover
V-Forve 4 reeds
Stock pipe/silencer
Slide-5 (no notch on front)
Needle Jet S4
Needle 42-74
Clip-2
Pilot 35
Main 500
AS - 1-1/2 turns
I switched from the VP MS-100 because I wanted to eliminate Oxy fuel from the equation and I can get AvGas for about half the price of MS-100.
Impression: Yeah , way crisper than stock. The main thing I noticed is how much faster the engine builds revs. It rips through it's rpm range so fast you have to be ready to shift quick. I could clear jumps tight out of corners much easier because the revs just spool up much quicker. It almost felt maybe a little too quick revving like it was a little lean. Going to try a 510 and 520 main next, possibly a 37.5 pilot, based on recommendations here. Obviously, if it feels borderline lean at 100 degrees that will only be compounded when temps drop.
Oh, I also tried going in to 1-3/4 on the PV spring and this didn't work well for me. It created a dip in the power or like the bike was falling on it's face due to the PV not opening as fast as the revs were building. This created some tricky situations if this dip would happen with bad timing on a jump approach.
Thanks to Digger and AJ565 for developing and refining these settings and everyone else who contributed with all the field testing. Saved me a bunch of time and money not having to figure it out myself!
By creating or opening up the notch on the front side of the slide , it causes the pilot circuit to function a little more efficiently, which in turn makes the first 30% or so of the throttle range a little richer. This is where it sounds like you want the bike to be a little richer.
I don't think you'll see much, if any difference after a 510 main. That main jet circuit is maxed out right about in that area, 510-515 range.
Tried the 42-73 needle first. It was definitely an improvement. I thought it was a little too crisp with the 42-74 and the 42-73 made that go away. Pulls stronger and steadier now.
Next I went from 500 to 520 on the main. Judging by all the charts I see, it appears genuine Mikuni jets jump in steps of 20 once you get above 500. In any case, I don't have a 510 so I put the 520 in. This also was an improvement. I've seen in earlier comments where AJ said a few times these bikes seem to like the fuel on top and can pull big mains. It definitely does. It still feels incredibly crisp and really screams. I ran out of time (and heat resistance) today but I want to try 540 and 560 mains to see if I can find the point of being too rich and work it back.
Overall I am pretty surprised how rich I am considering these high temps and some elevation. I'm thinking this is because of the AvGas. In the past on other bikes I've generally had to go a few sizes bigger on the main when running AvGas.
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